Adult stem cells reside in many different tissues of humans and other organisms. Their function is to provide a source of new cells to replace cells that are lost due to normal aging or tissue damage. Adult stem cells are maintained as stem cells by signals that come from the tissue surroundings where they live, called the niche. There is great interest in understanding how adult stem cells are maintained by their niches, so that these stem cells can be manipulated (boosted or inhibited), depending on the needs of the individual, either directly in the body or in the laboratory. Adult stem cells are difficult to stuy in humans, and even in other mammals, so simpler example niches have been studied in model organisms such as fruit flies. We study one of the best characterized model niches, the stem cells that support spermatogenesis in fruit flies (Drosophila). Many current ideas about how adult stem cells functions have arisen from studies of this niche. We are particularly interested in a gene named zfh-1 that is important in the stem cells of Drosophila testes, and this is the focus of this grant proposal. The homologous genes in humans and other mammals (called ZEB factors) are also required in certain stem cell populations, so this gene has a conserved role in regulating stem cells. Interestingly, this gene also promotes cancer progression and metastasis, so ZEBs/zfh-1 regulates multiple types of undifferentiated cells. Thus, we are very interested in understanding the molecular mechanisms that zfh-1 uses to promote the undifferentiated state. In this proposal we will take findings from the role of ZEB factors in cancer cells and during development, and test whether these are normal functions that are required in stem cells. We will focus on whether zfh-1 regulates two signaling pathways that cells use to communicate with each other; the TGF signaling pathway in Aim 1, and the receptor tyrosine kinase receptors and their intracellular signaling pathways in Aim 2. Both of these pathways function in the testis stem cells, and they are both involved in cancer cell metastasis. Our experiments will involve genetic manipulation in Drosophila, as well as tissue culture studies. Our findings on how zfh-1 acts to promote the undifferentiated state will be of interest to both stem cell and cancer biology.